But Robin Williams, a professor of molecular cell biology at Royal Holloway University of London, and his colleagues found out that the drug helps the brain produce a chemical that plays a key role in helping neurons communicate.

During a seizure, the amount of that chemical, called PIP3,drops. Valproic acid helps the brain make more PIP3and presumably helps the neurons resume normal communication.

That change, Williams tells Shots, seems to keep the "electrical storm" of a seizure from sweeping through the brain.

That's the good news. The bad news is that valproic acid is far from an ideal drug. People have long known it can damage the liver and pancreas. The Food and Drug Administration also warns of birth defects if it's taken by pregnant women.

Understanding how valproic acid works, Williams says, opens the door to finding out what other drugs might boost PIP3 without the dangerous side effects of valproic acid.

Those treatments won't be here anytime soon, says neurologist Cynthia Harden, with North Shore-LIJ Health System in Great Neck, N.Y.

"Discovering a new way valproic acid affects the brain isn't world-changing," Harden told Shots. "If it leads to something later down the line, from a clinical point of view it could make a significant contribution."

This study was conducted in rats, so it's not assured that the process is the same in humans. This finding also doesn't answer the question of how an epileptic seizure starts. "That's the holy grail of epilepsy research," says Williams.

But with 1 in 26 people in the U.S. developing epilepsy at some point in life, Williams says that there is a huge need for better treatments.